QuestionQuestion

Hydrology and surface flow
TASK 1
A 25 m wide rectangular storm drainage channel is lined in concrete and has a slope of 0.1%. It is 300 m long and has a freefall outlet. The channel drains an area of 1 ha and a recent event was observed across the catchment, characterized by a net precipitation of intensity i= 1.5 cm/h for 20 minutes. Consider a runoff coefficient of 0.35.

Evaluate
a. the uniform flow depth as generated by the meteorological event peak flow, considering the uniform flow conditions over the channel (10)
b. the depth at a section where 90% of uniform flow depth is achieved, considering unsteady state conditions for the same event (10)
c. Draw the water profile, justify your choice of profile and explain which conditions is the safest to evaluate the channel freeboard (10)

TASK 2
A catchment of 100 ha has the following unit hydrographs
time [minutes] 0    10    20    30    40      50      60    70         80
q m³/s/mm       0      2      4    6    4.80    3.60   2.41   1.21      0
and receives a net precipitation of intensity 3 cm/h for 10 minute.
A second catchment of 50 ha has the following unit hydrograph
time minutes   0      10      20    30    40    50    60    70    80      90      100 110    120    133.35
q m³/s/mm    0.00   0.60 1.20   1.80 2.40 3.00 2.64 2.28 1.92   1.56    1.20    0.84    0.49       0
but receives a net precipitation of 1 cm for 10 minutes, 10 minutes after the 1st catchment.

Assuming that at the peak flow the BOD5 from diffuse pollution for the first catchment BOD5 = 35 g/m3 and the second catchment has a BOD5 of 0.020 kg/m3 ; considering at the merging point a temperature of 15C and a combined dissolved oxygen concentration of 9 mg/L; considering a decay rate constant 0.18 day-1and the re-aeration rate constant to be and 0.475 day-1 respectively.

Calculate:
a. the first, second peak flow hydrograph using the unit hydrograph provided before and considering the precipitation received in each catchment (5)
b. the combined peak flow and total runoff, combined time to peak and time to end (10)
c. the combined BOD0 at the junction, location of minimum DO and distance of minimum DO from the junction considering the peak flows calculated in point (a) for both rivers and assuming a river velocity downstream of the junction of 0.2 m/s (10)
d. Provide the rest of assumptions necessary to calculate c.

TASK 3
Respond 5 multiple choice questions. Use the answer book clearly stating the question number and the corresponding letter. Each correct answer is worth 7 points. Each wrong answer will subtract 1 point from the total, unless the total score is negative.
1. Calculate the alternative depth corresponding to a specific energy of E= 14 m, a depth of 10 m and Froude number of 0.7.
a. 28 m
b. 10.62 m
c. 5.31 m
d. 1 m

2. Calculate the conjugate depth for a hydraulic jump in a rectangular channel considering an upstream depth of 0.7 m and an upstream Froude number of 5.
a. 4.61 m
b. 4.96 m
c. 9.22 m
d.    70 m

3. Which of the following definitions best defines a hydraulic jump:
a. a rapid varied flow transition from an upstream supercritical flow into a subcritical flow
b. a gradually varied flow observed in correspondence of drops.
c. a gradually varied flow transition from an upstream supercritical flow to a subcritical flow
d. a rapid varied flow transition from a upstream subcritical flow to a supercritical flow

4. Evaluate the peak flow for the following catchment: A=200 ha, runoff coefficient= 0.5, precipitation intensity 1 cm/hr.
a. 1 m3/s
b. 5.5 m3/s
c. 2.75 m3/s
d. 0.275 m3/s

5. Which of the following best describe diffuse pollution?
a. It is caused by single identifiable source of pollution from which pollutants are discharged, such as a pipe, ditch, ship or factory smokestack
b. It can be caused run-off from farmland, roads, houses and commercial areas
c. It does not depend on the area a catchment but only on the precipitation intensity
d. It a phenomena that is observed only in large catchments and in close proximity of rivers.

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Hydrology And Surface Flow Hydrology And Surface Flow
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